The published literature reports the presence of small numbers of microorganisms in donor blood at the time of collection. As shown in Table 1, Myhre et al. have detected the presence of from 1 to 8 bacterial strains at the time of phlebotomy, with some strains being present at concentrations greater than 25 organisms per ml. Myhre et al., "Bacteriocidal Properties of Platelet Concentrates," Transfusion 14:116 (1974).
TABLE 1 ______________________________________ Organisms Isolated From the First 7 mL of Donated Blood From Nine Normal Donors Bacterial Con- Occurrence centration Bacteria (N = 9) (org/ml) ______________________________________ Diptheroid sp. 1 10 colonies/7 ml Staph. epid. 6 1-200+ Bacillus sp. 9 1-200+ Micrococcus 1 4 Staph. aureus 4 1-100+ Neisseria sp. 2 1-100+ alpha. strep. 2 2-100+ Staph. sp. 1 1 ______________________________________
While there may be bacteria present at the time of blood collection, the presence of clinically significant numbers of bacteria at the time of transfusion is rarely encountered. For many years, this decline in the number of bacteria in donor blood between time of collection and the time of transfusion has been attributed to a sterilizing activity of white blood cells and plasma factors. See, for example, Buchholz et al , "Bacteria Proliferation in Platelet Products Stored at Room Temperature," NEJM 285:429 (1971); and Punsalang et al , "Growth of Gram-Positive and Gram-Negative Bacteria in Platelet Concentrates," Transfusion 29:596 (1989)
The occurrence of transfusion-induced sepsis is considered less likely with stored red blood cells (which are refrigerated during storage at about 4 degrees C.), compared to platelet concentrates (which are stored at room temperature). Still, there have been reports of sepsis caused by transfusions of refrigerated red blood cells with the organism Yersinia enterocolitica (which will be referred to as "Yersinia"). Yersinia is a human pathogen that can multiple in blood even during refrigerated storage at 4 degrees C. The occurrence of sepsis due to the presence of Yersinia in stored blood products is very rare, with only about twenty-three cases reported in the United States in the last nine years. Still, it would be desirable to completely eliminate its occurrence altogether.